81 x 9 = 801. What must you do to make the this equation true?

An American nightclub called 'The Coconut Grove' had a terrible fire in which over 400 people died. A simple design flaw in the building led to a high death toll. Subsequently, regulations were changed to ensure that all public buildings throughout the country eliminated this one detail, which proved deadly. What was it?

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

What does the following represent?

N N N N N N N

A A A A A A A

C C C C C C C

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?

What brings you down but never up?

There are forty elephants and they have forty-fore heads. How can this be possible?

I am a seven-letter word but if you remove four of my letters I will have one left. What word am I?

I get hot but I never sweat,
I cook food but I am not a chef,
I have a door but you can't enter me,
I have a light but I am not a lamp.
Who am I?

What runs around the whole yard without moving?